When did we start signing our names to authenticate documents?

Slate tech columnist Farhad Manjoo argued recently that the fax machine lives on largely because of our attachment to the written signature. Manjoo’s observation piqued the Explainer’s curiosity: When did scribbling your name on a piece of paper become a means of authentication?

A long time ago. Signatures on written transactions have been customary in Jewish communities since about the second century and among Muslims since the Hegira (the migration of Muhammad and his followers to Medina) in 622. In Europe, the signature dates to the sixth century. But it didn’t catch on widely there for another thousand-odd years, until the 16th and 17th centuries, when education and literacy were on the rise and more agreements were made in writing. In England, the 1677 Statute of Frauds—which stipulated that contracts must exist in writing and bear a signature—was pivotal. Signatures became a standard form of validating agreements—a practice that was also adopted in colonial America. …